1. Field
The present disclosure is directed to additive compositions and lubricating oils containing amine quaternary salts. In particular, it is directed to additive compositions and lubricating oils containing amine quaternary salts as friction modifiers for reducing one or both of thin film friction and boundary layer friction.
2. Description of the Related Technology
To ensure smooth operation of engines, engine oils play an important role in lubricating a variety of sliding parts in the engine, for example, piston rings/cylinder liners, bearings of crankshafts and connecting rods, valve mechanisms including cams and valve lifters, and the like. Engine oils may also play a role in cooling the inside of an engine and dispersing combustion products. Further possible functions of engine oils may include preventing or reducing rust and corrosion.
The principle consideration for engine oils is to prevent wear and seizure of parts in the engine. Lubricated engine parts are mostly in a state of fluid lubrication, but valve systems and top and bottom dead centers of pistons are likely to be in a state of boundary lubrication. The friction between these parts in the engine may cause significant energy losses and thereby reduce fuel efficiency. Many types of friction modifiers have been used in engine oils to decrease frictional energy losses.
Improved fuel efficiency may be achieved when friction between engine parts is reduced. Thin-film friction is the friction generated by a fluid, such as a lubricant, moving between two surfaces, when the distance between the two surfaces is very small. It is known that some additives normally present in engine oils form films of different thicknesses, which can have an effect on thin-film friction. Some additives, such as zinc dialkyl dithio phosphate (ZDDP) are known to increase thin-film friction. Though such additives may be required for other reasons such as to protect engine parts, the increase in thin-film friction caused by such additives can be detrimental.
Reducing boundary layer friction in engines may also enhance fuel efficiency. The motion of contacting surfaces in an engine may be retarded by boundary layer friction. Non-nitrogen-containing, nitrogen-containing, and molybdenum-containing friction modifiers are sometimes used to reduce boundary layer friction.
WO 96/18709 discloses a soap-based lubricant composition for use in belts or chain conveyers, comprising at least one soap dispersant of the formula:
where R6 is R or R—CONH—(CH2)n, R is a linear, branched, saturated or unsaturated alkyl residue having 8 to 22 carbon atoms or a corresponding alkoxy residue, R7 and R8 are the same or different alkyl or hydroxyalkyl substituents. This dispersant is also disclosed in EP 0988358.
US 2012/0010112 discloses acid-free quaternized nitrogen compounds and their use as a detergent additive, a wax anti-settling additive or an additive for reducing internal diesel injector deposits for fuels and lubricants. The quaternized nitrogen compounds are represented by the formulae:

US 2011/0303182 discloses a marine cross-head two-stroke diesel cylinder lubricating oil composition to achieve enhanced corrosive wear control in these engines.
US 2007/0032389 discloses a friction control composition including a binder, a rheological control agent and a lubricant.
U.S. Pat. No. 4,416,789 teaches a lubricant composition for a high density information disc. The lubricant composition comprises methyl alkyl siloxane and a long chain alkyl substituted betaine having the formula:
wherein R3 is a long chain alkyl group of 6-20 carbon atoms, R4 is hydrogen or alkyl group of 1-3 carbon atoms, and z is an integer.
US 2011/0098203 discloses a lubricant composition for resin conveyers, which comprises a nonionic surfactant, water and optionally a cationic surfactant and/or an amphoteric nonionic surfactant. Examples of amphoteric surfactants include surfactants of an alkyl betaine type, an amidobetaine type, and an imidazoline type. Species of surfactants include lauryl betaine, 2-alkyl-N-carboxynethyl imidazolinium betaine and 2-alkyl-N-carboxyethyl imidazolinium betaine.
US 2012/0138004 discloses detergent additives for fuels. One additive is quaternary ammonium salt that is the reaction product of (a) a non-quaternized amide and/or ester detergent having a tertiary amine functionality; and (b) a quaternizing agent. These additives may be derived from non-quaternized polyisobutylsuccinamides and/or esters, which are detergents that have tertiary amine functionality and an amide and/or ester group. The additives are essentially free of any additional acid component other than the acid group(s) present in the structure of the detergent itself.
In recent years there has been a growing desire to employ lubricating oils to provide higher energy-efficiency, especially lubricating oils that reduce friction. The present disclosure provides improved lubricating oils that may reduce one or both of thin film friction and boundary layer friction.